Digital integrated circuits perform various logic operations using elementary functional cells. Each one of these cells performs elementary operations and transfers the results of these operations to the adjacent cells to which it is connected. These elementary cells comprise various logic gate structures or structures derived therefrom.
The electric power supplied to the various cells is applied to each of the cells through supply rails that are located at metallization levels that are close to the functional areas of each cell. These rails are generally assembled in pairs and are brought to reference potentials which are generally ground (GND) and a reference voltage that is generally positive but depends on the particular technology used.
It has been observed that reliability problems may affect components because of electromigration phenomena that occur in the conductors that transport currents which have a significant current density.
In fact, electromigration phenomena cause the displacement of atoms inside the metallic conductors due to the impact of electrons. This displacement of atoms can result, in the long-term, in the appearance of areas that are devoid of material within a conductor.
In this case, the useful cross-sectional area of the conductors is therefore reduced and this increases the current density in the remaining cross-section and consequently increases the risks of electromigration. Conduction can, in extreme cases, be limited to the periphery of the conductor in barrier regions with a consequent significant increase in electrical resistance and associated temperature rises.
When electromigration phenomena occur directly above or below connection vias with upper and/or lower metallization levels, conduction can be totally interrupted if the cavity that is created covers the entire interface area between the conductor and the connection via.